Instrument material holder and method of fabrication thereof

ABSTRACT

A housing for a material holder includes an intermediate housing member having a generally horizontal member, an upper recess and a lower recess, an upper housing member having a generally horizontal member and a wall defining a material holding chamber, the upper housing member being seated within the upper recess of the intermediate housing member, and a lower housing member having a generally horizontal member, the lower housing member being seated within the lower recess of the intermediate housing member. The upper recess, the generally horizontal member of the intermediate housing member and the generally horizontal member of the upper housing member define a first cavity adapted to receive a first winding assembly, and the lower recess, the generally horizontal member of the intermediate housing member and the generally horizontal member of the lower housing member define a second cavity adapted to receive a second winding assembly.

FIELD OF THE INVENTION

The present invention relates generally to an improved holder formaterials used in measuring instruments such as calorimeters and to animproved fabrication method therefor, and more particularly to animproved holder and an improved fabrication method therefor which isparticularly suited for use in conjunction with a differential scanningcalorimeter.

BACKGROUND OF THE INVENTION

The present invention particularly relates to a material holder used ina differential scanning calorimeter of the type disclosed and claimed inU.S. Pat. No. 3,732,722 (“the '722 patent”) for a “Material Holder”issued May 15, 1973 to Norem et al. and assigned to The Perkin-ElmerCorporation of Norwalk, Conn. The entirety of the '722 patent isincorporated by reference herein.

A differential scanning calorimeter is a thermal analytical instrumentwhich operates on the principle that thermal energy is absorbed orevolved during physical or chemical changes in a material which is beinganalyzed. The differential scanning calorimeter measures thedifferential energy changes that occur in a sample material as comparedto a reference material, during such physical or chemical changes. Thesample material and a thermally inert reference material are placed inseparate material holders in the same thermal environment and theirtemperatures are measured during the analysis process.

The material holder, as disclosed in the '722 patent, includes acylindrical cup having three bottom partitions forming two cavitieswithin the bottom portion of the cup, one of the cavities containing aheating winding, and the other cavity containing a heat-sensing winding.A supporting center post is attached to the bottom of the lowermostpartition as a support for the material holder.

In order to produce the material holder, a series of substantiallyidentical discs are punched from sheet stock with a punch and die set toform the three partitions. These discs are successively press fittedinto a cylindrical housing and electron beam welded at the disc edges tothe cylindrical housing. The heater and sensing windings are sandwichedbetween the successive disc partitions.

Serious problems have been encountered in the above-described assemblyand fabrication method in that it has been found to be extremelydifficult to maintain tolerances on the disc diameters and the insidediameters of the cylindrical housings with sufficient precision to avoidvery high rejection rates in the assembled material cups. The success ofthe instrument resides in maintaining extreme precision. The precisionin measurement is so important that a noble metal such as platinum,paladium, gold, and their alloys are preferably used as the material ofthe material holder. Preferably, the metal of which the holder is formedis an alloy of 80% platinum and 20% iridium. The noble metals avoid theproblems of oxide formation.

The high precision also requires extremely narrow tolerances in theassembled dimensions of the material holders. Thus, in a material holderwhich is on the order of one-third of an inch in diameter (actually0.360 inches in one preferred embodiment), the various partitions mustbe perfectly parallel with one another with a variation out ofparallelism not to exceed 0.001 inch. Also, the various partitions mustnot be distorted in shape, the compartments containing the windings mustbe absolutely consistent and uniform in size, within the tolerance ofplus or minus seven ten thousandths of an inch, and there must be verygood conductivity between the edges of the partition discs and thecylindrical housing. In order to accomplish these purposes, thepartitions must be press fitted into position within the cylindricalhousing with a tight enough fit to precisely maintain the position ofeach disc during handling after assembly and before electron beamwelding. Furthermore, the press fit must be sufficiently tight topromote the production of a good sound electron beam weld between thedisc partition and the cylindrical housing in order to provide aconsistently high thermal conductivity through the joint formed thereby.On the other hand, the disc must not be press fitted with so much of aninterference fit that it results in distortion of the disc.

One of the biggest problems in achieving the satisfactory press fit ofthe disc partitions into the cylindrical housing apparently arisesbecause of variations in the diameters of the discs produced by thepunch and die set. For a particular batch run of approximately 900 discsbetween sharpenings of the punch and die set, it has been discoveredthat the disc diameters may vary in a typical range of about {fraction(3/10,000)}ths of an inch, or more. These variations in disc diameterare believed to be associated with the wear pattern of the punch anddie, and also, possibly, these variations may be related to variationsin the toughness and thickness of the sheet metal from which the discsare punched.

Another problem in providing the correct press fit arises particularlyin connection with the bottommost disc partition to which the supportpost is welded. It has been discovered that the support post weldingcauses the disc to which it is welded to shrink somewhat in diameter,that shrinkage being in the order of 4 to 5 ten thousandths of an inch.

Another major problem in producing a satisfactory press fit of the discpartitions has been found to result from the fact that the electron beamwelding of the first (uppermost) partition into the cylindrical housingcauses the diameter of that housing to shrink slightly, so as toincrease the tightness of the cylinder around the edges of subsequentlyassembled disc partitions. Similarly, the electron beam welding of thesecond disc partition causes still a further shrinking of thecylindrical housing for the assembly of the third disc partition.

These problems were substantially obviated by U.S. Pat. No. 4,330,933(“the '933 patent”) for a “Fabrication Method For Instrument MaterialHolder” issued May 25, 1982 to Bullinger et al. and assigned to ThePerkin-Elmer Corporation of Norwalk, Conn. The entirety of the '933patent is incorporated by reference herein.

The '933 patent teaches an improved fabricating method which compensatesfor at least part of the fluctuations in disc diameters, and whichcompensates for the shrinkage of the cylindrical housing during electronbeam welding of the first disc which includes the steps of sorting thediscs according to diameter into at least two sets including a first setand another set having diameters smaller than the discs of the firstset. Cylindrical housings are then machined with an inside diametersomewhat smaller than the outside diameters of the discs of the firstset to provide a press fit of the discs of the first set within thehousings. After press fitting and electron beam welding of a disc fromthe first set within each cylinder housing, one of the discs from thesmaller diameter set is press fitted into the housing, the smallerdiameter of the disc compensating for the shrinkage of the cylindercaused by the welding of the first disc.

In another aspect of the invention disclosed in the '933 patent, animproved fabrication method may be provided in which the discs aredivided into at least two sets, including a first set and another set ofdiscs which are larger in diameter than the discs of the first set. Abatch of cylindrical housings are then machined with an inside diameterto provide a desired press fit of the discs of the first set within thehousings. After a disc from the first set is press fitted into acylindrical housing and welded therein, one of the larger diameterdiscs, to which a supporting center post has already been welded, ispress fitted into the end of the cylindrical housing. The reduction inthe diameter of the last mentioned disc caused by the welding of thecenter post compensates for the larger initial diameter of the disc andthe reduction in the diameter of the cylindrical housing caused by thewelding of the earlier disc into the housing.

The above mentioned fabrication processes may be combined into a singleprocess in which the initial run of discs is sorted by diameter into afirst set, another set of discs having a diameter smaller than the discsof the first set, and still another set of discs having a diameterlarger than the discs of the first set, the discs of the first set beingused as the first disc partition to be positioned and welded into eachcylindrical housing, the inside diameter of which has been machined toprovide the appropriate press fit, the smaller diameter discs being usedas the second partition to be press fitted and welded into each housing,and the larger diameter discs being the ones to which supporting postsare attached prior to press fitting and welding into the cylindricalhousing to provide the third partition.

While the improved fabrication processes disclosed in the '933 patentobviate many of the problems with the processes disclosed in the '722patent in that the fabrication processes disclosed in the '933 patentavoid the problems arising from variations in the disc diameters asproduced by the punch and die, avoid the problem associated with theshrinkage in the diameter of the bottommost disc partition occasioned bythe welding of the support post thereto, and avoid the consequences ofthe problem of the shrinkage of the cylindrical housing resulting fromthe electron beam welding of earlier assembled disc partitions in orderto improve the press fit of subsequently assembled disc partitions, thefabrication processes disclosed in the '933 patent suffer fromdisadvantages of their own.

More specifically, the processes disclosed in the '933 patent are verylabor intensive to ensure proper spacing, requiring the use of precisiontooling fixtures and pins. Even when the operator is extremely careful,it difficult to accurately control the spacing of the heater and thesensor, and it is difficult to achieve reproducibility and consistentperformance characteristics between material holders. Moreover, thematerial holders disclosed in the '933 patent are comprised of arelatively high number of parts, and result in a high rate of scrapmaterial (on the order of 40% to 50%) due to the fact that the heaterand sensor assemblies are assembled to the center section from each end.Furthermore, using the processes disclosed in the '933 patent, it isdifficult to accurately know where to place the weld with the electronbeam welder, which can result in spluttered platinum in the opencavities.

What is desired, therefore, is a holder for materials used in measuringinstruments and a fabrication method therefor which requires less laborintensive processes than are currently employed, which ensures properspacing without requiring the use of precision tooling fixtures andpins, which allows for the spacing of the heater and the sensor to beaccurately controlled, which facilitates reproducibility and consistentperformance characteristics between material holders, which has areduced number of parts, which has a reduced scrap rate, and whichfacilitates the accurate placement of the electron beam weld so as toinhibit spluttered platinum in the open cavities.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aholder for materials used in measuring instruments and a fabricationmethod therefor which requires less labor intensive processes than arecurrently employed.

Another object of the present invention is to provide a holder formaterials used in measuring instruments and a fabrication methodtherefor having the above characteristics and which ensures properspacing without requiring the use of precision tooling fixtures andpins.

A further object of the present invention is to provide a holder formaterials used in measuring instruments and a fabrication methodtherefor having the above characteristics and which allows for thespacing of the heater and the sensor to be accurately controlled.

Still another object of the present invention is to provide a holder formaterials used in measuring instruments and a fabrication methodtherefor having the above characteristics and which facilitatesreproducibility and consistent performance characteristics betweenmaterial holders.

Yet a further object of the present invention is to provide a holder formaterials used in measuring instruments and a fabrication methodtherefor having the above characteristics and which has a reduced numberof parts.

Still a further object of the present invention is to provide a holderfor materials used in measuring instruments and a fabrication methodtherefor having the above characteristics and which has a reduced scraprate.

Yet another object of the present invention is to provide a holder formaterials used in measuring instruments and a fabrication methodtherefor having the above characteristics and which facilitates theaccurate placement of the electron beam weld so as to inhibit splutteredplatinum in the open cavities.

These and other objects of the present invention are achieved in oneembodiment by provision of a holder for materials for use in a measuringinstrument. The holder includes an intermediate housing member, an upperhousing member and a lower housing member. The intermediate housingmember includes a generally horizontal member, an upper wall extendingupwardly from an upper surface of the generally horizontal member, and alower wall extending downwardly from a lower surface of the generallyhorizontal member. The upper wall defines a first recess adjacent theupper surface having a first diameter and a second recess adjacent thefirst recess having a second diameter, the second diameter being greaterthan the first diameter, while the lower wall defines a third recessadjacent the lower surface having a third diameter and a fourth recessadjacent the third recess having a fourth diameter, the fourth diameterbeing greater than the third diameter. The upper housing member includesa generally horizontal member and a wall extending upwardly from anupper surface of the generally horizontal member, the wall defining amaterial holding chamber. The upper housing member is seated within thesecond recess of the intermediate housing member. The lower housingmember includes a generally horizontal member, and is seated within thefourth recess of the intermediate housing member. A first windingassembly is disposed within a first cavity defined by the first recess,the generally horizontal member of the intermediate housing member andthe generally horizontal member of the upper housing member, and asecond winding assembly is disposed within a second cavity defined bythe third recess, the generally horizontal member of the intermediatehousing member and the generally horizontal member of the lower housingmember.

In certain embodiments, the upper housing member has an outer diameterwhich is generally equal to or slightly larger than the second diameterof the second recess so as to create a frictional fit between theintermediate housing member and the upper housing member. Similarly, incertain embodiments, the lower housing member has an outer diameterwhich is generally equal to or slightly larger than the fourth diameterof the fourth recess so as to create a frictional fit between theintermediate housing member and the lower housing member.

Preferably, the intermediate housing member and the upper housing memberare electron-beam welded together and the intermediate housing memberand the lower housing member are electron-beam welded together. In someembodiments, the first winding assembly includes a pair of oppositelyarranged lead-out connector ribbons and the upper wall of theintermediate housing member includes a pair of oppositely arranged slotsto allow the lead-out connector ribbons to emerge therethrough.Similarly, in some embodiments, the second winding assembly includes apair of oppositely arranged lead-out connector ribbons and the lowerwall of the intermediate housing member includes a pair of oppositelyarranged slots to allow the lead-out connector ribbons to emergetherethrough.

In certain embodiments, the second recess of the intermediate housingmember has a beveled upper edge so as to facilitate insertion of theupper housing member therein, and/or the fourth recess of theintermediate housing member has a beveled lower edge so as to facilitateinsertion of the lower housing member therein. In some embodiments, aninner surface of the wall of the upper housing member includes ashoulder therein which is arranged to receive and support a cover.

Preferably, the upper housing member, the intermediate housing memberand the lower housing member are formed from an alloy comprising about80% platinum and about 20% iridium. In some embodiments, one of thefirst winding or the second winding comprises a heating winding and theother of the first winding or the second winding comprises aheat-sensing winding. In certain embodiments, the holder also includes acenter post and a washer member attached to the lower housing member.

In another respect, the present invention is directed to a housing for amaterial holder. In these embodiments, the housing includes anintermediate housing member having a generally horizontal member, anupper recess and a lower recess, an upper housing member having agenerally horizontal member and a wall defining a material holdingchamber, the upper housing member being seated within the upper recessof the intermediate housing member, and a lower housing member having agenerally horizontal member, the lower housing member being seatedwithin the lower recess of the intermediate housing member. The upperrecess, the generally horizontal member of the intermediate housingmember and the generally horizontal member of the upper housing memberdefine a first cavity adapted to receive a first winding assembly, andthe lower recess, the generally horizontal member of the intermediatehousing member and the generally horizontal member of the lower housingmember define a second cavity adapted to receive a second windingassembly.

In certain embodiments, the upper housing member has an outer diameterwhich is generally equal to or slightly larger than a diameter of aportion of the upper recess so as to create a frictional fit between theintermediate housing member and the upper housing member. Similarly, insome embodiments, the lower housing member has an outer diameter whichis generally equal to or slightly larger than a diameter of a portion ofthe lower recess so as to create a frictional fit between theintermediate housing member and the lower housing member.

Preferably, the intermediate housing member and the upper housing memberare electron-beam welded together and the intermediate housing memberand the lower housing member are electron-beam welded together. In someembodiments, the upper recess of the intermediate housing member has abeveled upper edge so as to facilitate insertion of the upper housingmember therein. Similarly, in some embodiments, the lower recess of theintermediate housing member has a beveled lower edge so as to facilitateinsertion of the lower housing member therein.

In certain embodiments, an inner surface of the wall of the upperhousing member includes a shoulder therein which is adapted to receiveand support a cover. Preferably, the upper housing member, theintermediate housing member and the lower housing member are formed froman alloy comprising about 80% platinum and about 20% iridium.

In yet another respect, the present invention is directed to a holderfor materials for use in a measuring instrument. The holder includes athree-piece housing consisting of an upper housing member, anintermediate housing member and a lower housing member, the three-piecehousing defining a first cavity and a second cavity. A first windingassembly is disposed within the first cavity and a second windingassembly is disposed within the second cavity.

Preferably, the intermediate housing member and the upper housing memberare electron-beam welded together and the intermediate housing memberand the lower housing member are electron-beam welded together. It isalso preferable that the upper housing member, the intermediate housingmember and the lower housing member are formed from an alloy comprisingabout 80% platinum and about 20% iridium. In certain embodiments, one ofthe first winding or the second winding comprises a heating winding andthe other of the first winding or the second winding comprises aheat-sensing winding. In some embodiments, the holder further includes acenter post and a washer member attached to the lower housing member.

In still another respect, the present invention is directed to a methodfor fabricating a holder for materials for use in a measuringinstrument. An intermediate housing member comprising a generallyhorizontal member, an upper recess and a lower recess is provided. Afirst winding assembly is disposed within the upper recess, and an upperhousing member comprising a generally horizontal member and a walldefining a material holding chamber is seated within the upper recess inorder to define, with the upper recess, the generally horizontal memberof the intermediate housing member and the generally horizontal memberof the upper housing member, a first cavity with the first windinghoused therein. A second winding assembly is disposed within the lowerrecess, and a lower housing member comprising a generally horizontalmember is seated within the lower recess in order to define, with thelower recess, the generally horizontal member of the intermediatehousing member and the generally horizontal member of the lower housingmember, a second cavity with the first winding housed therein.

The method preferably further includes the steps of electron beamwelding the intermediate housing member and the upper housing membertogether and electron beam welding the intermediate housing member andthe lower housing member together. In some embodiments, the methodfurther includes the step of creating a bevel in an upper edge of theupper recess of the intermediate housing member has so as to facilitateinsertion of the upper housing member therein and/or the step ofcreating a bevel in a lower edge of the lower recess of the intermediatehousing member has so as to facilitate insertion of the lower housingmember therein. In some embodiments, the method further includes thestep of creating a shoulder in an inner surface of the wall of the upperhousing member, which shoulder is adapted to receive and support acover.

The invention and its particular features and advantages will becomemore apparent from the following detailed description considered withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side isometric view of a holder for materials used inmeasuring instruments in accordance with an embodiment of the presentinvention;

FIG. 2 is a top plan view of the holder for materials used in measuringinstruments of FIG. 1;

FIG. 3 is a side elevational view of the holder for materials used inmeasuring instruments of FIG. 1;

FIG. 4 is a partially cross-sectional side view of the holder formaterials used in measuring instruments of FIG. 1;

FIG. 5 is a side elevational view of an intermediate housing member ofthe holder for materials used in measuring instruments of FIG. 1;

FIG. 6 is a partially cross-sectional side view of the intermediatehousing member of FIG. 5;

FIG. 7 is a top plan view of the intermediate housing member of FIG. 5;

FIG. 8 is a partially cross-sectional side view of an upper housingmember of the holder for materials used in measuring instruments of FIG.1;

FIG. 9 is a top plan view of the upper housing member of FIG. 8;

FIG. 10 is a partially cross-sectional side view of a lower housingmember of the holder for materials used in measuring instruments of FIG.1; and

FIG. 11 is a top plan view of the lower housing member of FIG. 10.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Referring first to FIGS. 1 through 4, a material holder 10 used inmeasuring instruments in accordance with the present invention is shown.The material holder 10 includes a housing 12 which defines a firstcavity 14 and a second cavity 16, the configuration of which isdescribed more fully below. Material holder 10 also includes a firstwinding assembly 18 which is intended to be housed within first cavity14 within the material holder 10 between adjacent partitions and asecond winding assembly 20 which is intended to be housed within secondcavity 16 within material holder 10 between adjacent partitions.

Each winding assembly 18, 20 includes a winding holder which preferablyconsists of a solid aluminum oxide chip upon which a platinum wirewinding is wound. A pair of platinum ribbons 22, 24 and 26, 28 aresoldered to the ends of the winding of each respective winding assembly18, 20 and serve as lead-out connectors. The lead-out connector ribbons22, 24, 26, 28 emerge through oppositely arranged slots 30, 32, 34, 36in the sides of the housing 12. Each winding assembly 18, 20 isinsulated from the adjacent partitions of the assembly by means ofinsulator discs (not shown), which may include tabs extending throughthe slots 30, 32, 34, 36 to insulate the lead-out connectors 22, 24, 26,28. The insulating layers may be formed, for example, of alumina clothto withstand high temperatures. Winding assemblies 18, 20 may comprise,for example, heater and sensor assemblies.

On the inside surface of the housing 12, in the upper portion thereof,there is a larger diameter portion terminating in a shoulder 38 which isarranged to receive and support a cover (not shown). The material to betested is supported upon the uppermost partition (more fully describedbelow) and enclosed within material holder 10 by the cover (not shown).

Attached to the bottom of the lowermost partition of housing 12 (morefully described below) is a center post 40. Center post 40 is attachedto the lowermost partition by means of a washer member 42. The centerpost 40 is first electron beam welded to the washer 42, and the washer42 is electron beam welded to the lowermost partition of housing 12.

Because the structure and function of the components described thus farabove in the “Detailed Description of an Embodiment of the Invention”section (in particular the configuration and operation of windingassemblies 18, 20) are well known to those skilled in the art andbecause further details of these components can be readily found invarious prior art references, for example in the '722 patent and the'933 patent (both of which are incorporated by reference herein), a moredetailed description of these components is not presented herein. Whatfollows is a detailed description of the novel elements of the presentinvention.

Rather than the housing being formed from a cylindrical outer housingmember and three press-fit discs, housing 12 of the present invention isformed from three components: upper housing member 44, intermediatehousing member 46 and lower housing member 48 (the cooperation of whichis best seen in FIG. 4). Upper housing member 44, intermediate housingmember 46 and lower housing member 48 are preferably formed from a noblemetal, such as platinum, paladium, gold, and their alloys. Mostpreferably, upper housing member 44, intermediate housing member 46 andlower housing member 48 are formed from an alloy of about 80% platinumand about 20% iridium.

Referring now to FIGS. 5 though 7 in addition to FIG. 4, intermediatehousing member 46 is shown in more detail. Intermediate housing member46 includes a generally horizontal member 50 which, when housing 12 isfully assembled as described more fully below, acts as an intermediatepartition for housing 12.

A wall 52 extends upwardly from an upper surface 54 of horizontal member50 about a periphery thereof, and defines a first vertical section 56.Wall 52 extends radially outwardly from first vertical section 56 todefine a horizontal section 58, and then wall 52 extends upwardly from aperiphery of horizontal section 58 to define a second vertical section60. Thus, as can be best seen in FIG. 6, intermediate housing member 46includes, on a top surface 54 of horizontal member 50 a wall 52 whichdefines a first recess 62 adjacent the top surface 54 having a diameterA and a second recess 64 adjacent the first recess 62 having a diameterB, the diameter B of the second recess 64 being greater than thediameter A of the first recess 62. Wall 52 includes a pair of oppositelyarranged slots 30, 32 as described above to allow lead-out connectorribbons 22, 24 to emerge from the housing 12 therethrough.

Intermediate housing member 46 also includes a wall 66 extendingdownwardly from a lower surface 68 of horizontal member 50 about aperiphery thereof, which wall 66 defines a first vertical section 70.Wall 66 extends radially outwardly from first vertical section 70 todefine a horizontal section 72, and then wall 66 extends downwardly froma periphery of horizontal section 72 to define a second vertical section74. Thus, as can be best seen in FIG. 6, intermediate housing member 46includes, on a bottom surface 68 of horizontal member 50 a wall 66 whichdefines a first recess 76 adjacent the bottom surface 68 having adiameter C and a second recess 78 adjacent the first recess 76 having adiameter D, the diameter D of the second recess 78 being greater thanthe diameter C of the first recess 76. Wall 66 includes a pair ofoppositely arranged slots 34, 36 as described above to allow lead-outconnector ribbons 26, 28 to emerge from the housing 12 therethrough.

Referring now to FIGS. 8 and 9 in addition to FIG. 4, upper housingmember 44 is shown in more detail. Upper housing member 44 includes agenerally horizontal member 80 which, when housing 12 is fully assembledas described more fully below, acts as an uppermost partition forhousing 12. A wall 82 extends upwardly from an upper surface 84 ofhorizontal member 80 about a periphery thereof. Wall 82 defines amaterial holding chamber 86.

On the inside surface of the wall 82, toward the upper end thereof,there is a larger diameter portion terminating in a shoulder 38 which isarranged to receive and support a cover (not shown). The material to betested is supported upon horizontal member 80 and enclosed withinmaterial holding chamber 86 by the cover (not shown).

Upper housing member 44 has an outer diameter E, at least toward thebottom portion thereof, which is dimensioned so as to be generally equalto, or slightly larger than, the diameter B of the second recess 64defined by wall 52 of intermediate housing member 46. This is desirableso that when housing 12 is fully assembled as described more fullybelow, there is little or no relative play, and preferably a frictionalfit, between upper housing member 44 and intermediate housing member 46.

Referring now to FIGS. 10 and 11 in addition to FIG. 4, lower housingmember 48 is shown in more detail. Lower housing member 48 generallycomprises a generally horizontal member 88 which, when housing 12 isfully assembled as described more fully below, acts as a lowermostpartition for housing 12.

Lower housing member 48 has an outer diameter F, at least toward the topportion thereof, which is dimensioned so as to be generally equal to, orslightly larger than, the diameter D of the second recess 78 defined bywall 66 of intermediate housing member 46. This is desirable so thatwhen housing 12 is fully assembled as described more fully below, thereis little or no relative play, and preferably a frictional fit, betweenlower housing member 48 and intermediate housing member 46.

The assembly of material holder 10 is now described. Winding assembly 18is disposed in first recess 62 defined by wall 52 of intermediatehousing member 46 such that lead-out connector ribbons 22, 24 emergethrough oppositely arranged slots 30, 32. The lower portion of upperhousing member 44 is then press-fit into the second recess 64 defined bywall 52 of intermediate housing member 46. Because upper housing member44 has an outer diameter E, at least toward the bottom portion thereof,which is dimensioned so as to be generally equal to, or slightly largerthan, the diameter B of the second recess 64 defined by wall 52 ofintermediate housing member 46, there is little or no relative play, andpreferably a frictional fit, between upper housing member 44 andintermediate housing member 46. The second recess 64 defined by wall 52of intermediate housing member 46 preferably has a beveled top edge 90(best seen in FIG. 6) so as to facilitate insertion of upper housingmember 44 therein.

The diameter A of first recess 62 defined by wall 52 of intermediatehousing member 46 is selected such that winding assembly 18 fitstherein. Moreover, the depth G of first recess 62 defined by wall 52 ofintermediate housing member 46 is selected such that winding assembly 18fits therein, and is preferably held snugly in the first cavity 14defined between horizontal member 50 of intermediate housing member 46and horizontal member 80 of upper housing member 44. The depth H ofsecond recess 64 defined by wall 52 of intermediate housing member 46 isselected to be deep enough that the frictional fit of upper housingmember 44 therein is maintained while material holder 10 is beingassembled, but is not so deep that an excessive force is required toseat upper housing member 44 therein.

Winding assembly 20 is disposed in first recess 76 defined by wall 66 ofintermediate housing member 46 such that lead-out connector ribbons 26,28 emerge through oppositely arranged slots 34, 36. At least the upperportion of lower housing member 48 is then press-fit into the secondrecess 78 defined by wall 66 of intermediate housing member 46. Becauselower housing member 48 has an outer diameter F, at least toward the topportion thereof, which is dimensioned so as to be generally equal to, orslightly larger than, the diameter D of the second recess 78 defined bywall 66 of intermediate housing member 46, there is little or norelative play, and preferably a frictional fit, between lower housingmember 48 and intermediate housing member 46. The second recess 78defined by wall 66 of intermediate housing member 46 preferably has abeveled lower edge 92 (best seen in FIG. 6) so as to facilitateinsertion of lower housing member 48 therein.

The diameter C of first recess 76 defined by wall 66 of intermediatehousing member 46 is selected such that winding assembly 20 fitstherein. Moreover, the depth I of first recess 76 defined by wall 66 ofintermediate housing member 46 is selected such that winding assembly 20fits therein, and is preferably held snugly in the second cavity 16defined between horizontal member 50 of intermediate housing member 46and horizontal member 88 of lower housing member 48. The depth J ofsecond recess 78 defined by wall 66 of intermediate housing member 46 isselected to be deep enough that the frictional fit of lower housingmember 48 therein is maintained while material holder 10 is beingassembled, but is not so deep that an excessive force is required toseat lower housing member 48 therein.

An electron beam welder is then applied to weld the various portions ofhousing 12, namely upper housing member 44, intermediate housing member46 and lower housing member 48 together.

The present invention, therefore, provides a holder for materials usedin measuring instruments and a fabrication method therefor whichrequires less labor intensive processes than are currently employed,which ensures proper spacing without requiring the use of precisiontooling fixtures and pins, which allows for the spacing of the heaterand the sensor to be accurately controlled, which facilitatesreproducibility and consistent performance characteristics betweenmaterial holders, which has a reduced number of parts, which has areduced scrap rate, and which facilitates the accurate placement of theelectron beam weld so as to inhibit spluttered platinum in the opencavities.

Although the invention has been described with reference to a particulararrangement of parts, features and the like, these are not intended toexhaust all possible arrangements or features, and indeed many othermodifications and variations will be ascertainable to those of skill inthe art.

1. A holder for materials for use in a measuring instrument, said holdercomprising: an intermediate housing member comprising: a generallyhorizontal member; an upper wall extending upwardly from an uppersurface of the generally horizontal member, the upper wall defining afirst recess adjacent the upper surface having a first diameter and asecond recess adjacent the first recess having a second diameter, thesecond diameter being greater than the first diameter; and a lower wallextending downwardly from a lower surface of the generally horizontalmember, the lower wall defining a third recess adjacent the lowersurface having a third diameter and a fourth recess adjacent the thirdrecess having a fourth diameter, the fourth diameter being greater thanthe third diameter; an upper housing member comprising a generallyhorizontal member and a wall extending upwardly from an upper surface ofthe generally horizontal member, the wall defining a material holdingchamber, the upper housing member being seated within the second recessof the intermediate housing member; a lower housing member comprising agenerally horizontal member, the lower housing member being seatedwithin the fourth recess of the intermediate housing member; a firstwinding assembly disposed within a first cavity defined by the firstrecess, the generally horizontal member of the intermediate housingmember and the generally horizontal member of the upper housing member;and a second winding assembly disposed within a second cavity defined bythe third recess, the generally horizontal member of the intermediatehousing member and the generally horizontal member of the lower housingmember.
 2. The holder of claim 1 wherein the upper housing member has anouter diameter which is generally equal to or slightly larger than thesecond diameter of the second recess so as to create a frictional fitbetween the intermediate housing member and the upper housing member. 3.The holder of claim 1 wherein the lower housing member has an outerdiameter which is generally equal to or slightly larger than the fourthdiameter of the fourth recess so as to create a frictional fit betweenthe intermediate housing member and the lower housing member.
 4. Theholder of claim 1 wherein the intermediate housing member and the upperhousing member are electron-beam welded together and wherein theintermediate housing member and the lower housing member areelectron-beam welded together.
 5. The holder of claim 1 wherein thefirst winding assembly comprises a pair of oppositely arranged lead-outconnector ribbons and wherein the upper wall of the intermediate housingmember includes a pair of oppositely arranged slots to allow thelead-out connector ribbons to emerge therethrough.
 6. The holder ofclaim 1 wherein the second winding assembly comprises a pair ofoppositely arranged lead-out connector ribbons and wherein the lowerwall of the intermediate housing member includes a pair of oppositelyarranged slots to allow the lead-out connector ribbons to emergetherethrough.
 7. The holder of claim 1 wherein the second recess of theintermediate housing member has a beveled upper edge so as to facilitateinsertion of the upper housing member therein.
 8. The holder of claim 1wherein the fourth recess of the intermediate housing member has abeveled lower edge so as to facilitate insertion of the lower housingmember therein.
 9. The holder of claim 1 wherein an inner surface of thewall of the upper housing member includes a shoulder therein which isarranged to receive and support a cover.
 10. The holder of claim 1wherein the upper housing member, the intermediate housing member andthe lower housing member are formed from an alloy comprising about 80%platinum and about 20% iridium.
 11. The holder of claim 1 wherein one ofthe first winding or the second winding comprises a heating winding andthe other of the first winding or the second winding comprises aheat-sensing winding.
 12. The holder of claim 1 further comprising acenter post and a washer member attached to the lower housing member.13. A housing for a material holder, said housing comprising: anintermediate housing member comprising a generally horizontal member, anupper recess and a lower recess; an upper housing member comprising agenerally horizontal member and a wall defining a material holdingchamber, the upper housing member being seated within the upper recessof the intermediate housing member; a lower housing member comprising agenerally horizontal member, the lower housing member being seatedwithin the lower recess of the intermediate housing member; wherein theupper recess, the generally horizontal member of the intermediatehousing member and the generally horizontal member of the upper housingmember define a first cavity adapted to receive a first windingassembly; and wherein the lower recess, the generally horizontal memberof the intermediate housing member and the generally horizontal memberof the lower housing member define a second cavity adapted to receive asecond winding assembly.
 14. The housing of claim 13 wherein the upperhousing member has an outer diameter which is generally equal to orslightly larger than a diameter of a portion of the upper recess so asto create a frictional fit between the intermediate housing member andthe upper housing member.
 15. The housing of claim 13 wherein the lowerhousing member has an outer diameter which is generally equal to orslightly larger than a diameter of a portion of the lower recess so asto create a frictional fit between the intermediate housing member andthe lower housing member.
 16. The housing of claim 13 wherein theintermediate housing member and the upper housing member areelectron-beam welded together and wherein the intermediate housingmember and the lower housing member are electron-beam welded together.17. The housing of claim 13 wherein the upper recess of the intermediatehousing member has a beveled upper edge so as to facilitate insertion ofthe upper housing member therein.
 18. The housing of claim 13 whereinthe lower recess of the intermediate housing member has a beveled loweredge so as to facilitate insertion of the lower housing member therein.19. The housing of claim 13 wherein an inner surface of the wall of theupper housing member includes a shoulder therein which is adapted toreceive and support a cover.
 20. The housing of claim 13 wherein theupper housing member, the intermediate housing member and the lowerhousing member are formed from an alloy comprising about 80% platinumand about 20% iridium. 21-25. (cancelled)
 26. A method for fabricating aholder for materials for use in a measuring instrument, said methodcomprising the steps of: providing an intermediate housing membercomprising a generally horizontal member, an upper recess and a lowerrecess; disposing a first winding assembly within the upper recess;seating an upper housing member comprising a generally horizontal memberand a wall defining a material holding chamber within the upper recessin order to define, with the upper recess, the generally horizontalmember of the intermediate housing member and the generally horizontalmember of the upper housing member, a first cavity with the firstwinding housed therein; disposing a second winding assembly within thelower recess; seating a lower housing member comprising a generallyhorizontal member within the lower recess in order to define, with thelower recess, the generally horizontal member of the intermediatehousing member and the generally horizontal member of the lower housingmember, a second cavity with the second winding housed therein.
 27. Themethod of claim 26 further comprising the steps of: electron beamwelding the intermediate housing member and the upper housing membertogether; and electron beam welding the intermediate housing member andthe lower housing member together.
 28. The holder of claim 27 furthercomprising the step of creating a bevel in an upper edge of the upperrecess of the intermediate housing member has so as to facilitateinsertion of the upper housing member therein.
 29. The holder of claim27 further comprising the step of creating a bevel in a lower edge ofthe lower recess of the intermediate housing member has so as tofacilitate insertion of the lower housing member therein.
 30. The holderof claim 27 further comprising the step of creating a shoulder in aninner surface of the wall of the upper housing member, which shoulder isadapted to receive and support a cover.
 31. A holder for materials foruse in a measuring instrument, said holder comprising: a three-piecehousing consisting of an upper housing member, an intermediate housingmember and a lower housing member, wherein the intermediate housingmember and the upper housing member are electron-beam welded togetherand wherein the intermediate housing member and the lower housing memberare electron-beam welded together, the three-piece housing defining afirst cavity and a second cavity; a first winding assembly disposedwithin the first cavity; and a second winding assembly disposed withinthe second cavity.